The present invention relates generally to evaporative emission control for a motor vehicle, and, more particularly, to an improved leak detection and control arrangement for an evaporative emission system of a motor vehicle.
In a conventional evaporative emission system, an emission control device is utilized to recover fuel vapor in a charcoal canister from a refueling event and selectively purge this fuel vapor from the charcoal canister into the engine. The emission control device is further utilized to perform leak detection tests to verify the integrity of the evaporative emission system and also provide pressure relief of the evaporative emission system. The emission control device is typically connected to an engine and a fuel tank and also includes a connection to the atmosphere. In general, conventional emission control devices provide control of various valves under specific engine operating conditions to perform system leak tests as well as system pressure relief. An example of such an evaporative emission system is disclosed in commonly owned U.S. Pat. No. 6,073,487 which is hereby incorporated by reference.
While such conventional systems work for their intended purpose, packaging of numerous system components and solenoids undesirably increase complexity and cost as well as typically require calibration for effective operation. Thus, there is a need for an evaporative emission system that overcomes the aforementioned and other disadvantages.
Accordingly, an evaporative emission control and leak detection system for a motor vehicle is provided. The system is in fluid communication with a fuel tank, an engine, and a carbon canister. The system includes an integrated valve module that is connected to the carbon canister and is in fluid communication with the atmosphere. The module is arranged to vent the system when exposed to predetermined high negative and positive pressure conditions, and a predetermined low negative pressure condition. The module includes a switch mechanism that is operable to indicate when the system is in a high or low negative pressure condition.
In accordance with another aspect of the present invention, the system can further include a low pressure valve and a high pressure valve with the valves being coupled in parallel to a fluid passage between the carbon canister and the atmosphere. The low pressure valve is arranged to provide low negative pressure system relief. The high pressure valve is a two-way valve arranged to provide both high positive and negative pressure system relief.